Such closure devices serve, for example, for the volumetric metering of free-flowing sample material, in order then to test a precisely defined quantity of the sample material for example in respect of composition and properties of the material. Such samples may consist of a wide variety of different materials, among which cement, clinker or for example broken slag may be mentioned merely by way of example. For metering purposes, the procedure is usually such that the free-flowing sample material is introduced in the first instance from above, in excess, into the filling chamber, which is closed initially on the underside for this purpose, and then a shut-off valve disposed at a certain filling-chamber height is pushed through the bulk material introduced, so that a metering chamber which is also closed off in the upward direction is formed in the filling chamber and the metered sample is thus separated off from the excess bulk material. The metering volume here results from the configuration and/or the hollow cross-section of the filling chamber and the spacing of the (upper) shut-off valve from the filling-chamber base. The latter may also be a shut-off valve which such as can be displaced from the closed position into the open position in order for the metered sample to be removed. In order to achieve as precise metering as possible, and to be able to displace the shut-off valve with only a low level of resistance through the bulk material introduced, shut-off valves made of the thinnest possible material, for example made of stainless-steel sheet with a thickness of approximately 1 to 2 mm, have proven successful. On the other hand, in particular thin-walled shut-off valves require guidance in the direction transverse to the displacement direction. In order to make precise metering possible the shut-off valve is accommodated in a longitudinally displaceable manner in a guidance gap in the peripheral region of the filling-chamber hollow cross-section, in particular upstream and downstream of the same, and the height of this gap is dimensioned such that deviations of the shut-off valve from the desired displacement plane are avoided as far as possible. If the shut-off valve is located in the open position, that length portion of the shut-off valve which follows the region with the through-opening, and projects beyond the hollow cross-section, is accommodated in a housing gap. In order to avoid the situation where sample particles (in particular sample dust) adhering to the shut-off valve also pass into the gap, attempts have been made to guide the shut-off valve by way of sealing elements which engage against the same and surround the hollow cross-section. However, this has the difficulty that certain sample materials have an abrasive action and could damage the seals and the shut-off valve over time. If the seals are not exchanged in good time, there is a risk of small quantities of the sample material nevertheless still penetrating into the housing gap. The fact that the sample material or the sample dust can collect there, finally penetrate out of the housing gap, which is open to the outside of the housing, and can also result in contamination outside is not considered to be the only disadvantage here. A further disadvantage, which is even more serious from an application point of view, is that, with sample materials changing, it may also be the case that a subsequent sample is contaminated, and thus impaired, by the previous sample.
With this in mind, it is an object of the invention for a closure device of the type mentioned in the introduction to be developed advantageously so that in particular the abovementioned disadvantages can be avoided as far as possible.